import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class UdpEchoServer {
    private DatagramSocket socket = null;
    public UdpEchoServer(int port) throws IOException {
        socket = new DatagramSocket(port);
    }
    public void start() throws IOException {
        System.out.println("服务器启动");
        //读取请求并解析
        while (true) {
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);
            String  request = new String(requestPacket.getData(),0, requestPacket.getLength());
            //根据请求计算响应
            String response = process(request);
            //把响应写回到客户端
            //构造UDP数据包
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(),0,response.getBytes().length,
                    requestPacket.getSocketAddress());
            //发送请求到客户端
            socket.send(responsePacket);
            System.out.printf("[%s %d] req = %s, resp =%s\n",requestPacket.getAddress(),requestPacket.getPort(),request,response);

        }

    }
    public String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer udpEchoServer = new UdpEchoServer(9090);
        udpEchoServer.start();
    }
}
